It is well known to prepare isocyanate terminated polyurethane prepolymers from polyether and or polyester polyols and aromatic diisocyanates. Furthermore, it is also well known to prepare polyurethane elastomers by chain extending these prepolymers with low molecular weight diols. The resulting polyurethanes have excellent mechanical properties, but are rather hydrophilic, which can limit their utility in certain moisture sensitive applications.
Hydroxyl terminated polyols with very non-polar backbones (e.g., hydroxyl functional polybutadiene) can be used to introduce hydrophobicity into polyurethane elastomers. However, the mechanical properties of the resulting polyurethane elastomers are generally rather poor when they are prepared using the conventional diisocyanates and diol chain extenders. In particular, they suffer from poor tear strengths and low elongation at break. In addition, the elastomers are opaque. This combination of properties limits their utility in applications requiring optical clarity or good resistance to tearing.
The modest mechanical properties of the polybutadiene containing polyurethane elastomers are probably at least partially due to the high functionality of the commercially available polybutadiene polyols (2.2 to 2.8 functional). In contrast, the polyether or polyester polyols used to make polyurethane elastomers with excellent mechanical properties generally have functionalities very near 2.0.
Hydroxy-terminated polybutadienes having a functionality of 2.0 are disclosed in Chung, et al. (U.S. Pat. No. 5,247,023), Grubbs, et al. (U.S. Pat. No. 5,750,815) and Nubel, et al. (U.S. Pat. Nos. 5,512,635, 5,559,190, 5,519,101 and 5,403,904). These diols, when formulated into polyurethane systems, may offer the opportunity to produce hydrophobic polyurethane elastomers with improved mechanical properties over the current state of the art.